As Lucifer's spawn, the world could be at your feet in seconds if you wanted to. The Winchesters had taken you in and Sam had started to teach you what it meant to be human, but to Dean you were still not one of them, you'd never be part of his family but a threat, not that he'd ever say it aloud, no. He was being rather passive about it, occasionally making a snarky remark here and there. It just seemed that he just didn't have the same level of patience towards you as he did towards his brother.